This application relates to an improved unloader valve being used to address system problems in a refrigerant cycle incorporating a scroll compressor.
Scroll compressors are becoming widely utilized in refrigerant compression applications. In a scroll compressor first and second scroll members each have a base and a generally spiral wrap extending from their respective bases. The wraps interfit to define compression chambers, and one of the scroll members is caused to orbit relative to the other. As the one scroll member orbits, the size of the compression chambers decreases, compressing the entrapped refrigerant.
Scroll compressors are incorporated into refrigerant cycles such that a condenser is typically positioned downstream of the scroll compressor, and expansion valve is positioned downstream of the condenser and a evaporator is positioned downstream of the expansion valve.
Several conditions within the refrigerant cycle can cause potential damage to the scroll compressor. First, if there is a loss of charge (i.e., some of the refrigerant has leaked out) then the suction pressure of the refrigerant entering the compressor may be lower than desirable. This may cause the compressor to compress the refrigerant to a discharge pressure such that the pressure ratio between the suction and discharge pressure is undesirably high. This can result in elevated temperatures within the compressor, which is undesirable. Other conditions which may lead to undesirable conditions within a scroll compressor are a fan failure, or other failures of components in the refrigerant cycle. Many methods have been proposed for addressing these types of failures. In general, these methods have addressed a single potential failure, rather than a broad range of failures. One additional problem in a scroll compressor occurs when the compressor motor is miswired to run in reverse. A scroll compressor running in reverse will pump the refrigerant from the discharge line into the suction line. With the refrigerant leaving the suction line, a good deal of lubricant will often migrate from the compressor. All of this is undesirable.
Scroll compressors have been provided with so called xe2x80x9cunloaderxe2x80x9d valves which selectively communicate a compressed refrigerant line to a suction line. As an example, unloader valves will often communicate the suction and discharge lines leading to and from the compressor. Typically, the unloader valve is positioned within the compressor housing.
In a few proposed compressors an unloader valve is positioned outwardly of the compressor housing to selectively communicate the suction refrigerant line to a more compressed point. These valves have typically been opened to achieve capacity control, or a reduction in the amount of refrigerant which is being compressed.
In the disclosed embodiment of this invention, Applicant positions an unloader valve outwardly of the compressor housing. The unloader valve is opened in response to a sensed refrigerant cycle failure. In this fashion, the refrigerant moving toward the compressor is supplemented by discharge refrigerant leaving the discharge port.
In a reverse rotation situation, this will allow the lubricant leaving the suction tube to be quickly returned to the discharge tube, as explained better below. In a loss of charge situation, this will provide supplemental refrigerant in addition to the lower quantity of refrigerant leading into the suction tube. This will alleviate much of the undesirable effect of the loss of charge situation. This arrangement will have benefits for many other system failures. Further, positioning the controls and the unloader valve on the exterior of the housing shell will make replacement or repair of these relatively delicate components much simpler than if they were positioned within the compressor shell.
In summary, the inventive use of an unloader valve located outside of the compressor housing combined with the inventive control provides a number of valuable benefits.
These and other features of the present invention can be best understood from the attached specification and drawing, the following of which is a brief description.